(a) Field of the Invention
This invention relates to an electronic control fuel injection system for a spark ignition internal combustion engine wherein fuel flow rate is determined by a depression amount of an accelerator pedal to thereby determine air flow rate and, more particularly, to a throttle valve actuating system in ignition type internal combustion engines provided with a computer which puts in output signals from various sensors detecting a selected fuel injection amount, engine operating state and environmental conditions and operates an air amount to be supplied adapted to the operating state of the engine at such time point and a throttle servo-mechanism including a throttle actuator which can determine a proper opening degree of a throttle valve from the results of the operation of this computer.
(b) Description of the Prior Art
Recently the spark ignition internal combustion engine of the above mentioned type has come to be highlighted as being provided with a new electronic control type fuel injection system. This shall be summarized with reference to FIGS. 1 and 2 in which the reference numeral 1 denotes an accelerator pedal, 2 denotes, for example, a potentiometer for converting the displacement of the accelerator pedal 1 to an electric signal, 3 denotes a fuel supply means, 4 denotes a metering means for metering the fuel supplied from the fuel supply means 3, 5 denotes an injector connected to the metering means 4 and fitted within an intake manifold bore 6, 7 denotes a throttle valve, 8 denotes a throttle actuator consisting of a miniature servo-motor connected to a throttle shaft 7a, for example, through a pulley-and-belt mechanism to determine the opening degree of the throttle valve 7, 9 denotes a potentiometer or encoder for converting the actuation amount of the throttle actuator 8, that is, the opening degree of the throttle valve 7 to an electric signal and 10 denotes a computer which includes a microprocesser, specific purpose input/output interface and memory, puts in output signals from the potentiometers 2 and 9, metering means 4, throttle actuator 8 and such various sensors detecting the engine operating state and environmental conditions as a suction air temperature sensor, fuel supply line pressure sensor, engine temperature sensor and throttle valve downstream pressure sensor, puts out command signals to the metering means 4 to secure a fuel injection amount selected by the displacement of the accelerator pedal 1 and concentrically controls the throttle valve opening degree and number of idling revolutions responding to the fuel injection amount to the optimum valves in conformity with the operating state of the engine so that, when the operator depresses the accelerator pedal 1, a signal put out of the potentiometer 2 in response to the depression amount of the accelerator pedal 1 will be put into the computer 10 and the computer 10 will operate a pulse width and/or frequency of the injector 5 by the operating state of the engine at that time, will determine the fuel delivery amount from the injector 5, will inject it into the intake manifold 6, will mix it with intake air and will feed the mixture into the combustion chamber of the engine. The computer 10 will put in information from the above mentioned various sensors in the form of a voltage, electric current, degital signal and/or frequency signal, will operate functional relations between them and the flow rate of intake air, will operate the optimum air amount at that time point, will put out the results in the form of electric signals to the throttle actuator 8 and will actuate them to bring the throttle value 7 to a required opening degree position. Meanwhile, the pressure difference between the upstream side and downstream side of the throttle value 7 will be always detected and, by this signal and a simultaneously detected throttle valve position signal, the computer 10 will always continue to operate the optimum value every moment and will put out commands to the throttle actuator 8. Further, the inflow air amount determined by the combination of the pressure difference between the upstream side and downstream side of the throttle valve and the throttle valve opening degree will be calibrated in advance and the functional relations will be memorized as mappings in the memory of the computer so that the signal from the above mentioned pressure difference sensor, the output to the throttle actuator 8 or the electric signal from the potentiometer or encoder connected to the throttle actuator 8 will be always compared with these memories and operated.
In the internal combustion engine of this kind of conventional type, as described above, the throttle valve 7 is indirectly opened and closed so as to always maintain the optimum opening degree by the output from the computer 10 but there have been defects that, in case the throttle actuator 8 consists of a miniature servo-motor or step motor and the throttle shaft 7a and motor shaft are connected with each other through such power transmitting means as a belt, gear or cam mechanism, not only the electric power consumption will increase but also the response delay will not be able to be avoided.